1. Field of the Invention
This invention pertains in general to the field of underground mining and, in particular, to a novel adaptation of continuous-miner development and retreat mining techniques for shortwall and longwall to recover underground reserves under shallow cover.
2. Description of the Related Art
Continuous underground mining is used to extract fossil fuels and other valuable minerals found in strata-bound deposits. Historically, underground mining is carried out by gaining access to the ore through entries developed from an exposed seam. This development is generally done from the point of interest at the surface, such as at an outcrop or from an exposed highwall resulting from surface mining. All mining utilities, ventilation, transportation of personnel, and removal of the mined material are carried in and out by utilizing such entries within the mineral seam. As a result, it has been conventional practice not to exploit with underground methods deposits having shallow cover with no highwalls or outcrop, or ones with reclaimed highwalls having spoils placed against them, or with highwalls or an outcrop left unsuitable for entry because of previous mining. It has been found that gaining underground entry to the seam through such unfavorable conditions would render the practice uneconomical under most circumstances. On the other hand, gaining entry to the seam through a vertical or inclined shaft results in significant cost increases that often also render the operation uneconomical. The expense of lowering belt and structure components, as well as electrical, hydraulic and pneumatic system parts, through the shaft and assembling them underground would be prohibitive. Therefore, there is a need for an efficient, economic and safe method of recovery of underground coal reserves under such conditions.
This invention is directed at providing an affordable approach to the exploitation of such shallow reserves by combining efficient seam-mining practices, such as the use of continuous miners, shortwall and longwall, with access to the reserve by means of a vertical shaft equipped with a novel continuous system for feeding infrastructure to the mining face. Thus, the invention materially enhances the feasibility of mining shallow reserves with no direct access to the seam.
The invention is described in the context of coal mining, but its principles are equivalently applicable to any material suitable for extraction with continuous mining equipment, such as lignite, oil shale, limestone, anthracite, trona, potash, halite, bauxite, gypsum, and other sedimentary rocks that host oxide, sulfide or carbonaceous gold ores and/or other poly-metallic minerals. Similarly, the invention is described in terms of a mine developed through a shaft, but it is equivalently applicable to mines where access to the reserves is obtained through entries within the ore seam.